Recruitment of oriens-lacunosum-moleculare interneurons during hippocampal ripples

Abstract

Sharp wave-associated ∼200-Hz ripple oscillations in the hippocampus have been implicated in the consolidation of memories. However, knowledge on mechanisms underlying ripples is still scarce, in particular with respect to synaptic involvement of specific cell types. Here, we used cell-attached and whole-cell recordings in vitro to study activity of pyramidal cells and oriens-lacunosum-moleculare (O-LM) interneurons during ripples. O-LM cells received ripple-associated synaptic input that arrived delayed (3.3 ± 0.3 ms) with respect to the maximum amplitude of field ripples and was locked to the ascending phase of field oscillations (mean phase: 209 ± 6°). In line, O-LM cells episodically discharged late during ripples (∼6.5 ms after the ripple maximum), and firing was phase-locked to field oscillations (mean phase: 219 ± 9°). Our data unveil recruitment of O-LM neurons during ripples, suggesting a previously uncharacterized role of this cell type during sharp wave-associated activity.

Fast network oscillations in the hippocampus

“…We have mostly worked on the experimental model system of hippocampal slices of mice (and rats). These ~400 μm thick slices, cut approximately along the laminar network structure, express activity patterns, entirely independent of external activation and resemble in vivo SPW-R with respect to many aspects: they emerge within CA3, propagate toward CA1 and the entorhinal cortex, display a similar laminar profile as has been described by Buzsáki et al Finally, the activation patterns of pyramidal cells and interneurons are very similar, as has been shown recently (e.g., see [28,42,51,52]). Obviously, the advantage of the in vitro preparation is the easy access for multiple recording techniques, in particular for high-resolution cellular recording techniques.…”

Using Multi-Compartment Ensemble Modeling As an Investigative Tool of Spatially Distributed Biophysical Balances: Application to Hippocampal Oriens-Lacunosum/Moleculare (O-LM) Cells

“…Depending on experimental protocol, an additional depolarizing (+90 pA) or hyperpolarizing (−90 pA) would then be applied for a 1 s duration, after which the additional depolarizing or hyperpolarizing current injection would cease. The depolarizing current stimulus would result in regular action potential firing in the observed O-LM cells, with a “saw-tooth” [67] firing profile typically seen in O-LM cells and a long-lasting afterhyperpolarization. The hyperpolarizing current stimulus results in a characteristic “sag” back towards the resting potential, attributable to the presence of the hyperpolarization-activated current, I h .…”

Early postnatal nicotine exposure disrupts the α2* nicotinic acetylcholine receptor-mediated control of oriens-lacunosum moleculare cells during adolescence in rats

“…The majority of these interneurons are somatostatin-positive oriens-lacunosum moleculare (OLM) cells (Jia et. al., 2009, 2010; Leao et al, 2012) that receive cholinergic inputs from the medial septum and are involved in the modulation of brain-state-specific network oscillations (Leao et al, 2012; Pangalos et al, 2013; Lovett-Barron et al, 2014). In the CA1, OLM cell dendrites extend horizontally within the stratum oriens, and their axons ramify extensively in the stratum lacunosum moleculare, where they innervate the distal dendritic tufts of pyramidal cells.…”